The present invention relates to a printing apparatus and, more particularly, to a printing apparatus which uses a printing medium such as paper having a continuous shape and is suitable to print a continuous print image, and a control method therefor.
Conventional printing apparatuses for printing an image on a printing medium (to also be simply referred to as printing paper hereinafter) such as a paper sheet, textile, plastic sheet, or OHP sheet use various print schemes, and printing apparatuses having printheads using the wire dot, thermal printing, heat transfer printing, or ink-jet methods have been proposed.
Of these schemes, the ink-jet method is one of noise-free non-impact methods of directly discharging ink to printing paper. The ink-jet methods are roughly classified into continuous types (including charged particle control and spray methods) and on-demand types (including piezo, spark, and bubble-jet types) depending on the ink droplet formation method and discharge energy generation method.
In the continuous types, ink is continuously discharged, and charges are applied to only necessary droplets. The charged droplets stick to printing paper, and the remaining droplets are wasted. To the contrary, in the on-demand type, ink is discharged only when it is necessary to print. For this reason, the ink is not wasted, and no contamination occurs in the apparatus. In addition, the response frequency for the on-demand type is lower than that for the continuous type because ink discharge is started or stopped. The number of nozzles is increased to realize high-speed printing. Most of currently commercially available printing apparatuses use the on-demand type. Printing apparatuses having an ink-jet printhead can print at high density and high speed and therefore are commercially available as output terminals for copying machines, facsimile apparatuses, word processors, or personal computers.
Generally, an ink-jet printing apparatus has a printhead, an ink tank for supplying ink to the printhead, a conveyor means for conveying printing paper, and a control means for controlling these elements. The ink-jet printhead which discharges ink droplets from a plurality of discharge ports is serially scanned in a direction perpendicular to the printing paper conveyance direction. While the head is not printing, the printing paper is intermittently conveyed by an amount equal to the print width. Since the ink is discharged onto the printing paper in accordance with a print signal, this printing method is popularly used as a noise-free print method at low running cost.
When a full-line type ink-jet printhead having nozzles aligned on an array corresponding to the width of printing paper is used, and the printing paper is continuously conveyed in a direction perpendicular to the nozzle array of the ink-jet printhead, printing in the paper width is performed. With this arrangement, the speed of printing can be further increased.
In a color ink-jet printing apparatus, a color image is formed by superposing ink droplets dischargeed from a plurality of color printheads. Generally, for color printing, four ink-jet printheads and ink tanks corresponding to three colors of yellow (Y), magenta (M), and cyan (C) or four colors additionally including black (Bk) are required. Currently, color printing apparatuses having such a plurality of color ink-jet printheads and capable of forming a full-color image have been put into practical use.
The energy generation means for generating an energy for causing the ink-jet printhead to discharge ink uses an electromechanical converter such as a piezo element or an electrothermal transducer having a heating resistor to heat the liquid.
Especially, an ink-jet printhead using a method (so-called bubble-jet) if discharging ink using a thermal energy (using a film boiling phenomenon) can have liquid discharge ports at high density, and can print a high-resolution image.
Demands for such ink-jet printing apparatuses have arisen in various fields. In the field of, e.g., geologic formation probing, an ink-jet printing apparatus is used to continuously print several meters or more of geologic formation data using a plurality of colors. In the apparel industry as well, an ink-jet printing apparatus is used to print on clothing materials. As described above, demands for ink-jet printing apparatuses have arisen in various industrial fields as an excellent printing means. It is also required to obtain a higher-quality image.
As described above, an ink-jet printing apparatus can also be applied to print a continuous print image having a length of several meters or more. In this case as well, a print image must always be stably printed at a predetermined print length, i.e., at the same print length as the precedingly output print image. For this purpose, the mechanical printing medium conveyance accuracy is conventionally improved.
In recent years, the resolution of an ink-jet printhead is largely increasing from 360 dpi to 600 or 720 dpi. However, the mechanical accuracy of the conveyor mechanism for conveying a printing medium has improved little, so the ratio of mechanical conveyance errors to the pixel pitch of the printhead is increasing. In printing an image of A4 size, the error in length of a print image is small. However, when one print image continues for several meters or more, mechanical conveyance errors accumulate, resulting in a large error in length of the print image.
The present invention has been made in consideration of the above problem, and has as its object to provide a printing apparatus which performs appropriate magnification processing for print image data to absorb any mechanical error of a conveyor mechanism, and a control method therefor.
It is another object of the present invention to detect any conveyance errors of the conveyor mechanism before print processing, thereby allowing setting of the correction amount by the above magnification processing.
It is still another object of the present invention to achieve the above magnification processing by increasing/decreasing the number of print lines, thereby further simplifying the arrangement.
It is still another object of the present invention to superpose data of a print line to be deleted on data of the next print line when reduction is performed as magnification processing, thereby reducing the loss of print information.
It is still another object of the present invention to detect any feed amount error of the conveyor mechanism during printing and to set the magnification amount of the print data on the basis of the feed amount error.
It is still another object of the present invention to obtain the magnification amount set on the basis of the feed amount error detected during printing with reference to a table in which the feed amount error and magnification amount are paired and registered, thereby allowing high-speed setting of magnification processing.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.